1. Field of the Invention
The present invention relates to a playback apparatus and a playback method for playing back streams in which subtitle data or button data is multiplexed with video data or audio data recorded on a large-capacity recording medium, such as Blu-ray DiSc™. The invention also relates to a playback program implementing the playback method.
2. Description of the Related Art
As the standards of disc-type recording media which are removable from recording/playback apparatuses, Blu-ray Disc standards have been proposed. According to the Blu-ray Disc standards, 12-cm discs having a cover layer of 0.1 mm are used as recording media, and objective lenses having a blue-violet laser of a wavelength of 405 nm and an numerical aperture of 0.85 are used as optical systems so that a maximum of 27 gigabytes (GB) recording capacity is implemented. This makes it possible to record Japanese-standard broadcasting satellite (BS) digital high-definition (HD) programs for more than two hours without deteriorating the image quality.
As the sources for supplying audio/video (AV) signals to be recorded on such optical discs, two types of sources are assumed: one type is a source for supplying analog signals transmitted by analog television broadcasting and the other type is a source for supplying digital signals transmitted by digital television broadcasting. According to the Blu-ray Disc standards, the standards for recording AV signals by the two types of broadcasting systems have already been defined.
As the derivative standards of the current Blu-ray Disc, read-only recording media on which movies or music are recorded are being developed. As disc-type recording media for recording movies or music, digital versatile discs (DVDs) have already been used widely. However, read-only optical discs based on the Blu-ray Disc standards are superior to known DVDs since they can record HD video for more than two hours while maintaining the high image quality by taking advantage of characteristics unique to the Blu-ray Disc, such as the large capacity and high transfer speed.
The standards of read-only recording media based on Blu-ray Disc are hereinafter referred to as the Blu-ray Disc Read-Only Memory Format (BD-ROM) standards.
One of the indispensable elements for the content recorded on read-only recording media is subtitles. In the BD-ROM standards, subtitles are displayed on a plane different from a plane on which a moving picture is displayed, and by combining the subtitle plane with the moving picture plane, the subtitles and the moving picture can be displayed by being superposed on each other. For example, the subtitle plane is overlaid on the moving picture plane, and in the subtitle plane, the portions other than the subtitles are made transparent. Then, one piece of image data in which subtitles are displayed on a moving picture can be formed.
To record the content, such as a movie, on a disc and offer the disc for sale as a package media, a user interface for controlling the execution of various programs that accompany the content is recorded together with the content on the disc. A typical user interface is a menu displayed on a screen. As an example of a menu displayed on a screen, buttons for selecting functions are provided as a button image, and the user can select and set one of the buttons through a predetermined input unit, and then, the function assigned to the selected button is executed. Generally, by using a cross key provided for a remote control commander compatible with a player, the user selects a button displayed on a screen and presses a setting key. Then, the function associated with the button is executed.
Japanese Unexamined Patent Application Publication No. 2004-304767 discloses the following techniques. In the technique disclosed in this publication, on the basis of recording/playback standards, i.e., the Blu-ray Disc standards (Blu-ray Disc Rewritable Format Ver1.0), a moving picture plane for displaying a moving picture and a subtitle plane for displaying subtitles are separately provided. Then, the moving picture based on video data and the subtitles based on subtitle image data are displayed together on one screen. Additionally, a technique for displaying a menu on a screen by the use of a button image is also disclosed.
According to the BD-ROM standards, video data or audio data is recorded on a disc in the form of a transport stream (TS), which is defined in Moving Pictures Experts Group 2 (MPEG2) systems. More specifically, video data or audio data is divided into packetized elementary stream (PES) packets, and the PES packets are further divided into portions having a predetermined size, and a header having identification information (packet identification (PID)) indicating the data type is appended to each divided portion. Then, a 188-byte TS packet is formed. The TS packets are then multiplexed and recorded on a disc.
The above-described subtitle image data and image data for displaying a menu screen or commands are also divided into PES packets according to a predetermined unit and are further divided into portions having a predetermined size. Then, header information having a PID is appended to each divided portion, resulting in a TS packet. The TS packets are then multiplexed with video data or audio data, and the multiplexed data is recorded on a disc.
Details of the recording of data on a disc are further given below in the context of subtitle image data. Subtitle image data is formed of units, which are divided by the breakpoints intended by the author, and each unit is stored in a PES packet. In this case, the subtitle image data includes a plurality of data items, such as the subtitles formed of, for example, bitmap data, information concerning where and how the subtitle image data are displayed, and information concerning the display frame that defines the frame of the subtitle image data. The plurality of data items are separately stored in the corresponding PES packets. A plurality of data items forming subtitle image data are hereinafter generically referred to as “subtitle image data”.
A decoding time stamp (DTS) and a presentation time stamp (PTS) indicating the decoding time and the display time, respectively, of subtitle image data filled into a PES packet are stored in a PES header, which is the header of the PES packet. The PES packet is further divided into portions having a predetermined size, and the PID indicating the data type is appended to each divided portion, resulting in a TS packet. The TS packet is then multiplexed with a TS packet of video data and audio data and a TS packet of button image data, which is discussed below, and the multiplexed packets are then recorded on a disc.
Data for displaying a menu screen is processed similarly to the subtitle image data. A plurality of data for displaying a menu screen are separately formed into PES packets, and then, the PES packets are divided into portions having a predetermined size. The PID is then appended to each divided portion, resulting in a TS packet.
To display the above-described subtitle image data by playing back the disc, the transport stream is read from the disc and the header is extracted from each TS packet to obtain the PID. The TS packets storing the subtitle image data are then separated on the basis of the obtained PIDs and are temporarily stored in a buffer. When a sufficient number of TS packets that can be reconstructed into a PES packet are stored in the buffer, data is extracted from the payloads of the same type of TS packets on the basis of the associated PIDs so that the PES packet is reconstructed. The PES header is then removed from the reconstructed PES packet, and a plurality of data forming the subtitle image data are reconstructed.
The reconstructed plurality of data forming the subtitle image data are temporarily stored in a decode buffer. The data is then read from the decode buffer at the time represented by the DTS stored in the PES header and are decoded. The decoded data is then stored in an output buffer. The data stored in the output buffer is output at the time represented by the PTS stored in the PES header.